Track shoe assembly for continuous track vehicles

ABSTRACT

An improved track shoe assembly ( 13 ) for a continuous track vehicle ( 1 ). The track shoe assembly comprises a pin ( 17 ) which is rotatable relative to the shoe assembly ( 13 ). The shoe assembly comprises an elastomeric tube ( 31 ) through which the pin extends, the elastomeric tube being rotatable with respect to one of the pin and the shoe assembly and being fixed with respect to the other of the pin and the shoe assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to, and claims priority from, United StatesProvisional Application Serial No. 61/172,755, filed 26 Apr. 2009, andU.S. application Ser. No. 12/650,296, filed 30 Dec. 2009, thedisclosures of which are hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

Continuous track vehicles (also known as “track laying” vehicles) arewell known and widely used. The present invention relates to suchvehicles and has particular applicability to military tanks. Theconstruction of military tanks and their tracks is well known and isdescribed for example in Cory, U.S. Pat. No. 4,765,694, Kent, U.S. Pat.No. 6,080,493, Soucy et al, U.S. Pat. No. 7,416,266, Gonzalez, U.S. Pat.No. 7,445,299, and Touchet et al, U.S. Pat. No. 5,264,290, thedisclosures of all of which are hereby incorporated by reference.

Briefly, a military tank typically includes two tracks, one on each sideof the vehicle. Each track has a road-engaging side and an inner sidewhich engages a set of road wheels, as well as a drive sprocket at theforward or rearward end of the vehicle, an idler wheel at the other endof the vehicle, and support rollers along an upper reach of the trackabove the road wheels. The track itself is formed of track shoeassemblies. Each assembly typically includes two track shoes, spacedlaterally from each other and separated by a center guide which guidesthe track around the road wheels, drive sprocket, idler wheel andsupport rollers. Each track shoe carries an elastomeric inwardly-facingroad wheel pad bonded to its inner face and an elastomericoutwardly-facing road pad removably mounted to its outer face. The padsare generally rubber, although composite pads have also been proposedfor the road pad.

Each track shoe assembly also includes two pin assemblies extendinglaterally across and beyond the track shoe assembly. The pin assemblieshold the two track shoes of each shoe assembly together in alignmentwith each other, and the ends of pin assemblies of adjacent shoeassemblies are connected by end connectors. In one modern arrangement,the center guide is mounted on the pin assemblies of adjacent shoeassemblies, so that a projection part of the center guide straddlesadjacent shoe assemblies, rather than being centered between the trackshoes of a single shoe assembly. Although metal bushings have been usedin tractor-type continuous track vehicles, as described for example byWright, U.S. Pat. No. 3,313,578, large continuous track vehicles, suchas military tanks, have used rubber bushings.

In a military tank or the like, each pin assembly includes a hollow pinin the form of a steel shaft drilled out to reduce its weight. Multiplerubber bushings are bonded to the exterior of the pin. Bonding istypically produced by injection molding the rubber onto the pin, andthen vulcanizing the rubber. The number of bushings shown in the patentliterature is generally two: one for each track shoe. In practice, sevenrubber “donuts” are bonded to the pin for each track shoe, givingfourteen rubber bushings for each pin assembly, in an arrangementsimilar to Krotz, U.S. Pat. No. 2,430,573. This arrangement allows therubber to compress and spread laterally (axially of the pin) when thepin assembly is forced into the shoe assembly. The rubber conventionallyhas a nominal hardness of about 75 A on the Shore hardness scale beforeit is compressed by about forty percent when pushed into the sleeve ofthe track shoe assembly. The force required to push the pin into theshoe assembly requires a thirty- to fifty-ton press. For many years, theart has taught that, “Such compression must be sufficient so that thereis no rotation between the bushing and the outer sleeve portions or thepin upon bending of the track during use.” (Cory, U.S. Pat. No.4,840,438 at col. 2, lines 9-12). This arrangement insures that“relative rotation therebetween [between the pin and the track shoe]along the length of the pin assembly is controlled by elasticdeformation of the resilient bushing.” (Id. at col. 13, lines 41-43).Because the rubber bushings are bonded to the pin, there has been noneed to machine the pin to close tolerances, and the pin may have avariation in diameter of as much as 0.5 mm (0.020″) and may deviatesubstantially from being linear. Conventional pin assembliesincorporating compressed bushings are disclosed in Knox et al, U.S. Pat.No. 1,955,751, Lamb, U.S. Pat. No. 1,973,214, Knox et al, U.S. Pat. No.2,089,210, Knox, U.S. Pat. No. 2,301,954, Saurer et al U.S. Pat. No.2,332,976, Krotz, U.S. Pat. No. 2,430,573, Reynolds et al, U.S. Pat. No.3,357,750, Huhne et al, U.S. Pat. No. 4,139,241, Fix, U.S. Pat. No.4,165,906, Ruddell, U.S. Pat. No. 4,195,887, and Wiesner, U.S. Pat. No.5,749,634, the disclosures of all of which are hereby incorporated byreference.

Cory, U.S. Pat. No. 4,840,438, discloses that the extreme compressionrequired by the conventional compressed bushings creates assemblyproblems and also “results in a greater resistance to the requiredbending during use and a consequent greater power requirement fordriving of the associated vehicle.” To solve this problem, Cory moldsand bonds the rubber bushing in situ to the pin and to a pair of sleevesections having a positioning flange which fits into a groove in theassociated track shoe when the bushing is compressed about 5% andpressed into the shoe assembly. The flange and groove prevent rotationof the pin assembly with respect to the shoe assembly, thereby insuringany relative rotation of the pin and shoe is controlled by elasticdeformation of the rubber. Cory's arrangement, however, addsconsiderable complexity and additional manufacturing requirements,thereby substantially increasing the cost of the track.

Particularly with heavy continuous track vehicles, such as militarytanks, the lifetime of the track is very short, frequently a few hundredmiles of use. When the track fails, the vehicle may become unusable. Thefailure of tank tracks creates a huge financial cost and may causelogistical issues and personnel safety issues. The problem isparticularly acute with tanks of the size of a Bradley Fighting Vehiclehaving a weight of greater than about twenty-five tons, an M-60 battletank having a weight greater than about fifty tons, or an Abrams M-1battle tank having a weight greater than about fifty tons to aboutseventy-five tons or more. The problem has long been known, as witnessedfor example by Ruddell, U.S. Pat. No. 4,195,887, filed 1978 (“Thecompressive and shear loads placed on the elastomeric bushings farexceed the capabilities of present elastomers to withstand these loadsand the elastomeric bushings wear out and must be replaced.”), Cory,U.S. Pat. No. 4,840,438, effectively filed 1985 (“The constantlyincreasing weight and speed of track laying vehicles has resulted in adecrease in the track life and a constant increasing need for trackmaintenance by either repair or replacement.”), or Kent, U.S. Pat. No.6,080,493, filed 1998 (“A complete set of tracks for a U.S. Army M-1Abrams tank can cost as much as $100,000.00 and may only last from 300to 2000 miles.”).

The problems with track life are two-fold. Although the inner road wheelpads apparently exhibit little wear, the outer road pads are subject tosubstantial wear and to hazards such as puncturing. They are thereforemade to be field replaceable. Second, and more seriously, the rubberbushings rapidly fail. In practice, the bushings generally fail beforethe road pads, so the entire track is frequently replaced before theroad pads can be field replaced. Replacing the entire track requiresremoving the tank to a repair facility via a tank carrier vehicle.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, the present invention provides an improved track shoeassembly for a continuous track vehicle.

In accordance with an embodiment of the invention, the track shoeassembly includes a pin which is rotatable relative to a shoe of thetrack shoe assembly. The preferred track shoe assembly includes twobushings; each bushing has a metal sleeve and an elastomeric tube bondedto the interior of the sleeve. Each sleeve is force-fit into a shoe ofthe track shoe assembly. The pin is pushed through the elastomeric tubesand in use rotates freely with respect to the elastomeric tube. Theelastomeric tube is preferably formed of polyurethane. The polyurethanein some embodiments has a Shore hardness of at least 60 D; in otherembodiments, the Shore hardness is between about 65 D and about 70 D; inyet other embodiments the Shore hardness is between about 95 A and 110A. Generally, the polyurethane is chosen to have excellent hysteresisproperties, that is, it does not build up substantial heat as it isstressed and released. In some embodiments, the sleeve is a DOM (drawnover mandrel) steel tube and has a wall thickness of about 0.76 mm toabout 2.5 mm (about 0.030″ to about 0.100″); in other embodiments thesleeve has a wall thickness of 1.5 mm (0.06″)±20%. In an illustrativeembodiment, the sleeve has a diameter of 50.8 mm (2.00″). In someembodiments, the elastomeric tube has a wall thickness of about 2.5 mmto about 6.4 mm (about 0.1″ to about 0.25″); in other embodiments, theelastomeric tube has a wall thickness of 5.1 mm (0.2″)±15%.

Because polyurethane, unlike rubber, internally relieves stresses,because the polyurethane is not prestressed by forcing the bushing intothe track shoe, because the bearing area of the polyurethane elastomeris greatly increased as compared with conventional rubber donuts, andbecause the polyurethane does not control the rotation of the pin withrespect to the shoes by elastic deformation, the bushings of the presentinvention will greatly outwear conventional rubber bushings. Thedecrease in differential stress produced by the shoe assemblies of thepresent invention extends not only to the bushings but to the pins andother components of the tracked vehicle, thereby increasing bothperformance and durability.

Because they do not limit rotation of the pin with respect to the shoe,the bushings of the present invention are also expected to reduce theenergy required to propel the vehicle, thereby increasing performanceand efficiency. The improvements produced by the present invention aremore remarkable in light of the long-standing belief that bonding of thebushings to prevent rotation with respect to both the pin and the shoeof the track is essential to operation of the track. The success of thepresent bushings also belies the belief that rotatable mounting of thepins would lead to standing waves in the upper reaches of the continuoustrack and early failure of the track.

In accordance with another embodiment of the invention, the pin ismachined, preferably centerless ground, to a tolerance of 0.0254 mm(0.001″), thereby permitting the pin to be inserted into the bushingsmounted in the shoes of the track shoe assembly with the use of ahand-held mallet or sledge. The pin is preferably made of 4340 steel,heat treated and shot peened for hardness, then drilled out to reduceits weight.

The bushing of the present invention is related to the bushingsdescribed in my prior patents, U.S. Pat. Nos. 4,840,395 and 5,988,614,the disclosures of which are hereby incorporated by reference. Themodified bushing of the present invention, however, has heretofore beenconsidered by those skilled in the art as unusable in a track shoeassembly of a heavy endless track vehicle.

In accordance with another embodiment of the invention, the road pad ofthe shoe is formed of polyurethane having good abrasion and punctureresistance and having a Shore hardness of about 90 A to 95 A. This padprovides far longer life than the rubber pad, despite having inferiorhysteresis characteristics. The hysteresis test is currently relied uponas the chief indicator of pad life.

In accordance with another embodiment of the invention, the road wheelpad is made of polyurethane having a Shore hardness of 95 A to 105 A,having good hysteresis characteristics, heat resistance, and punctureresistance.

The foregoing and other objects, features, and advantages of theinvention as well as presently preferred embodiments thereof will becomemore apparent from the reading of the following description inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the accompanying drawings which form part of the specification:

FIG. 1 is a view in side elevation of a conventional pin assembly foruse in the continuous track of an M-1 tank.

FIG. 2 is a view in side elevation of a pin and bushings of the presentinvention for use in the continuous track of an M-1 tank.

FIG. 3 is a view in upper side perspective of two adjacent shoeassemblies of the present invention.

FIG. 4 is a top plan view of two adjacent shoe assemblies of the presentinvention showing their inner, road wheel pads.

FIG. 5 is a perspective view of a blank for a bushing for use with thepin and track shoe assemblies of FIGS. 2-4.

FIGS. 6A and 6B are perspective and end views, respectively, of a castand machined-steel track shoe for use in the present invention, beforebonding of a road wheel pad to its top, installation of a road pad toits bottom, and installation of bushings.

FIG. 7 is a perspective view of a road pad of the present invention.

FIGS. 8A and 8B are views in side elevation of an M-1 tank and an M-60tank, respectively, in which embodiments of the present invention may beused.

Corresponding reference numerals indicate corresponding parts throughoutthe several figures of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description illustrates the invention by way ofexample and not by way of limitation. The description clearly enablesone skilled in the art to make and use the invention, describes severalembodiments, adaptations, variations, alternatives, and uses of theinvention, including what is presently believed to be the best mode ofcarrying out the invention.

As shown in FIG. 8A, an Abrams M-1 tank 1 includes, on each side, roadwheels 3, a drive sprocket 5 at the rear of the vehicle, an idler wheel7 at the front of the vehicle, and support rollers 9 along an upperreach of the track above the road wheels. A continuous track 11 passesaround these wheels, sprockets and rollers and drives the tank 1. TheM-60 tank 1′ shown in FIG. 8B is similar, but has six road wheels 3′ andhas its drive sprocket 5′ at its forward end. Because the M-60 tanklacks the side armor of the M-1 tank, its support rollers 9′ arevisible.

The track 11 is made up of track shoe assemblies 13. Each shoe assembly13 includes two shoes 15 mounted side by side on pins 17.

In this embodiment, the pins 17 are about sixty-five cm (25.5″) long and38.1 mm (1.5″) in diameter. The pins are provided with flats 19 neartheir ends to accommodate standard track shoe assembly end connectors21. Each pin is formed of a steel shaft drilled out to reduce itsweight.

A center guide 23 is mounted on the pins of adjacent shoe assemblies, sothat a projection part 25 of the center guide straddles adjacent shoeassemblies, rather than being centered between the track shoes of asingle shoe assembly.

As thus far described, the construction is that of a standard militarytank, well known in the art for many years.

In the prior art construction shown in FIG. 1, a pin assembly includes asteel pin 17′ with fourteen rubber donut bushings 27 bonded to the pin17′. In accordance with the present invention, the pin assembly whichhas heretofore been pressed into the track shoes is replaced withbushings 31 pressed into the track shoes and a modified pin 17 which ispushed through the bushings and rotates freely with respect to thebushings during operation of the tank.

Each bushing 31 is formed of an outer sleeve 33 and a polyurethane tube35 bonded to the inside of the sleeve 33. In some embodiments, in whichside load is expected, the end of the sleeve 33 may be turned inwardsufficiently to prevent or restrain movement of the polyurethane axiallybeyond the end of the sleeve 33. The sleeve 33 is a DOM (drawn overmandrel) low carbon steel tube. The sleeve 33 has a length of 22.9 cm(9″) and has a wall thickness of 1.9 mm (0.075″) and an outer diameterof 50.80 mm (2.000″). Although the wall thickness of the sleeve 33 isnot critical, the outer diameter of the sleeve 33 is chosen to give aline-to-line fit with a tubular opening in the shoes 15 as describedbelow. The polyurethane tube 35 is formed and bonded to the sleeve 33 bysand-blasting the inner surface of the tube, applying a bonding agent,and pouring liquid polyurethane into the sleeve, around a centralmandrel. The central opening in the polyurethane tube is then bored outto 38.10 mm (1.500″) diameter. The polyurethane material is chosen tohave low hysteresis (low internal heating with repeated stresses andreleases) and an unstressed hardness of Shore 60 D to 70 D. A suitablematerial is sold by ITWC, Inc., Malcom, Iowa, 50157, US, and isidentified as ATRO PL07, having a hardness of 65 D. Another suitablematerial is sold by UET, LLC, Peoria, Ariz., 85345, as its 8001-A-82%,having a hardness of 62 D. The PLOT material has been shown to have aload-deflection curve similar to that of the rubber conventionally usedin tank track bushings.

The track shoe 15 is conventionally made of a cast steel shoe body 37having a lower face to which a road pad is bolted and an upper face towhich a road wheel pad is bonded. The body 37 includes a bolt hole 39for accepting a bolt of the road pad and two cylindrical openings 41which accept and hold the pin assemblies of a conventional shoeassembly. The track shoe 15 of the invention is modified by boring outthe openings 41 to give them a true and uniform diameter of 5.090 cm(2.004″). Because the openings 41 and bushings are 22.9 cm (9″) long,the fit between them is tight, requiring on the order of ten to twentytons of pressure to install them and providing no rotation between thebushing and the shoe 15.

The modified pin 17 is made of 4340 steel, heat treated and shot peenedfor hardness, and drilled out to reduce its weight. The outside diameterof the pin 17 is machined by centerless grinding, to exactly 38.1 mm(1.5″) in diameter with a tolerance of about 0.0254 mm (0.001″), therebypermitting the pin to be inserted into the bushings mounted in the shoes15 of the track shoe assembly 13 with the use of a hand-held mallet orsledge. The pin 17 is conventionally 64.8 cm (25.5″) long and has flats19 ground near each end, to accept conventional connectors 21 whichassemble the track.

The removable road pad 51 bolted to each shoe 15 is formed to the samedimensions as a conventional rubber road pad, but is formed ofpolyurethane having good abrasion and puncture resistance and having aShore hardness of about 92 A. This pad provides far longer life than therubber pad, despite having inferior hysteresis characteristics. Thehysteresis test is currently relied upon as the chief indicator of padlife.

The road wheel pad 53 bonded to each shoe 15 is made of polyurethanehaving a Shore hardness of 95 A to 105 A, having good hysteresischaracteristics, heat resistance, and puncture resistance.

Numerous variations in the track shoe assemblies, bushings, pads, andpins of the present invention, within the scope of the appended claims,will occur to those skilled in the art. Merely by way of example, theelastomeric tube 35 could be bonded directly to the opening 41 of theshoe and the sleeve 33 omitted. This arrangement would require moreaggressive removal of the elastomer, as by boring or burning, in orderto rehabilitate the bushing, but would permit the wall of the opening 41to be made thicker if desired. The shoe 15 may be slightly enlarged, orthe diameter of the pin 17 may be slightly reduced in order to increasethe thickness of the opening 41, of the elastomeric tube 35, or of thesleeve 33.

For use with track laying vehicles such as the Bradley Fighting VehicleSystem in which the pin is conventionally non-circular, the elastomerictube 35 can be bonded to the pin and made rotatable with respect to thesleeve 33. Alternatively, an enlarged circular-cross section can beprovided on the central part of the pin, as by utilizing a modified pinor fitting a sleeve over the central part of the conventional pin.

As various other changes could be made in the above constructionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

All patents and patent applications mentioned herein are herebyincorporated by reference.

1-10. (canceled)
 11. An improved track shoe assembly for a continuoustrack vehicle, the track shoe assembly comprising a road pad formed ofpolyurethane having good abrasion and puncture resistance and having aShore hardness of about 90 A to about 95 A.
 12. The shoe assembly ofclaim 11 wherein the pad provides longer life, in use on a vehiclehaving a weight in excess of twenty-five tons, than a conventionalrubber pad having superior hysteresis characteristics.
 13. The shoeassembly of claim 11 wherein the shoe assembly comprises at least oneshoe, the shoe comprising a shoe body, the road pad being attached to alower face of the shoe body.
 14. The shoe assembly of claim 13 whereinthe shoe body is a casting.
 15. The shoe assembly of claim 13 whereinthe road pad is bolted to the shoe body.
 16. The shoe assembly of claim13 wherein a road wheel pad is attached to an upper face of the shoebody.
 17. The shoe assembly of claim 16 wherein the road wheel pad isbonded to the shoe body.
 18. The shoe assembly of claim 13 wherein theroad wheel pad is formed of polyurethane.
 19. The shoe assembly of claim18 wherein the road wheel pad has a Shore hardness of 95 A to 105 A. 20.The shoe assembly of claim 13 wherein the track shoe assembly comprisestwo shoes, each shoe having a shoe body and a road pad attached to theshoe body, each road pad being made of polyurethane having a Shorehardness of about 90 A to about 95 A.
 21. A continuous track vehiclehaving a track composed of shoe assemblies of claim
 11. 22. The vehicleof claim 21 wherein the vehicle has a weight in excess of abouttwenty-five tons.
 23. The vehicle of claim 22 wherein the vehicle has aweight in excess of about fifty tons.